This invention relates to the manufacture of electrical devices and more particularly to an improved electrical device.
Various types of electrical devices comprise electrical components such as semiconductors, resistors (thick and thin film), hybrid microcircuit devices and the like are disposed within the interior of a protective package or housing, and the interior of the package is normally provided with a suitable inert atmosphere. The package conventionally comprises a base portion and a lid portion, with the functioning electrical components being carried on the base portion and the lid being permanently fastened onto the base by suitable sealing methods such as welding, soldering or adhesives such as epoxy resins and the like.
During the manufacturing process it is often possible for particles to become entrapped in the interior of the package or housing protecting the functioning electrical components. For example, lint particles can sometimes be found in such devices, as well as particles introduced as a result of the sealing operations. Under certain circumstances such particles, which can become mobile within the protective package, can result in shortening the life of the electrical component and, in many cases may result in the complete malfunctioning of the devices. Devices manufactured for the avionics and space industry and for the military normally are subjected to particle impact noise detection (PIND) tests such as represented by MIL-Std 883, Method 2020 under which the device is subjected to impact and agitation and the movement of particles within that package detected. Accordingly, the presence of particles of any type within the interior of the sealed package of an electrical device is considered highly deleterious and can result in a substantial number of rejected units and a substantial increase in the cost per unit for manufacture.
A variety of methods have been proposed and utilized to alleviate the particle problem in devices utilizing sealed packages. For example, great care has been utilized in the processing itself to avoid the production of particles and to reduce the possibility of such particles being in the atmosphere at the time of sealing the package of the device. In certain cases a small resealable opening is provided in the package for removal of particles after manufacture of the electrical device. After removing the particles the opening in the package is resealed. Needless to say, the foregoing methods require extreme care during the manufacturing operations and, in many cases, are ineffective in the prevention of particles within the package of the electrical device.
Other methods involve the coating of the electrically active areas within the device either before or after sealing to immobilize particles which may be trapped therein and to render the circuits electrically immune to the action of conductive particles. Such methods can raise the manufacturing costs substantially and also can result in failures if conductive particles are immobilized in a critical area so as to affect the functioning of the electrical device.
The use of "getter" materials within the interior of the package of an electrical device has been suggested generally for entrapment of moisture and/or various harmful gases. However, North, in U.S. Pat. Nos. 2,988,676 and 2,987,799 suggests the use of a chemically inert material that becomes tacky upon heating for trapping particles immediately following production of a semiconductor device. These materials, however, are generally deficient in that they normally do not have the properties of a particle getter at normal ambient temperatures and such materials are generally not useful over a wide range of temperatures.
It has been reported that experimental investigation has been conducted into the use of high purity cured silicone as a "particle getter" in sealed package electrical devices. R. S. F. David, Proc. Electron Components Conf., Anaheim, Calif., Apr. 24-26, 1978, IEEE, New York (1978). As will be seen, however, fully cured silicone material has not proven successful under the test conditions set out hereinafter.
The present invention overcomes the foregoing deficiencies in sealed package electrical devices with respect to foreign particles.